With the progress of science and technology, the number of types of mobile devices has increased. More and more users not only carry smartphones, tablets and other devices, but also wear smart wristbands, smart watches, smart glasses and other wearable devices. Some (such as the smartphones) of such devices can access the Internet anytime and anywhere through a cellular communication module, but most of the time, as a wireless local area network (WLAN) has advantages of a low cost (free in many places), a high speed and low energy consumption, access to the Internet through Wi-Fi or Bluetooth becomes a better choice for many devices. In fact, some telecom operators also deploy a large number of WLAN access points (APs) in hotspot regions of a city, so as to improve the network bandwidth available to users or offload a cellular network. Generally, in a process where the user searches for an AP in order to access a WLAN through the AP, authentication is required and related operations may be very inconvenient.